1. Technical Field
The present invention relates to a secondary battery, and more particularly, to a balancing device and method for enabling various balancing modes for a plurality of battery cells connected in series.
2. Related Art
In general, a secondary battery is a battery that is capable of storing energy through a charging process and using the stored energy at the outside of the battery through a discharging process. A battery cell constituting a secondary battery may be limited in voltage due to chemical or structural problems. Accordingly, in application fields in which a high voltage is necessary, a secondary battery in which a necessary number of battery cells are connected in series is used. Even when battery cells are manufactured under the same manufacturing conditions and the same environments, the battery cells differ from each other in electrical characteristics. In addition, while the battery cells are being used, there may be a difference even in a degree that the internal properties of batteries are deteriorated. Accordingly, even when the battery cells are charged and discharged with the same current, an imbalance in a voltage or an imbalance in a remaining amount of charge between the battery cells connected to each other may occur.
When the voltage of a battery cell is too high, there is a danger of a fire or an explosion. In contrast, when the voltage of a battery cell is too low, the characteristics of the battery cell may be lost. In order to prevent such problems, when any one of a plurality of battery cells is overcharged or over-discharged, charging or discharging of the entire battery cells may be controlled. That is to say, when some of a plurality of battery cells connected in series are overcharged more than the other battery cells, charging of the battery cells is interrupted in a state in which the other battery cells have not been sufficiently changed. In contrast, when some of the battery cells are over-discharged, use of the battery cells is restricted in a state in which the other battery cells yet have usable energy.
When the imbalance in a voltage or the imbalance in a remaining amount of charge between the battery cells connected in series occurs, as described above, the usable voltage range of the battery cells is reduced or the charging and discharging periods are shortened, thereby shortening the lifecycle of the battery cells. In order to overcome such problems, balancing methods for uniformly maintain the voltages and the amounts of charge of battery cells have been suggested.
The conventional balancing methods for battery cells may be largely classified into a passive method for performing balancing of battery cells while consuming energy and an active method for performing balancing of battery cells while not consuming energy.
The passive balancing method is inefficient because overcharged energy is consumed through a resistor in order to balance energy between battery cells. For this reason, more researches have been conducted on the active balancing method.
The active balancing method may be classified into a method of using a magnetic element, such as a transformer or an inductor, as an energy transfer medium, and a method of using a capacitor as an energy transfer medium.
Recently, balancing of battery cells has been required to reduce the manufacturing cost and the size thereof using a small number of switching elements, and simultaneously, to enable various modes.